S1W2 L1- Circulatory Physiology- Cardiac excitation-contraction coupling- Ruth Norman Flashcards
Ca2+ induced Ca2+ release architecture of the t-tubules and SR cross bridge cycling filament structure actin myosin interaction and the Prescence of Ca2+ Ca2+ recycling
what does EC-CC describe
converting electrical stimulus to mechanical response
t-tubule
extensions of plasma membrane which invaginate into the centre of cardiac cells (typically around z discs)
SR
sarcoplasmic reticulum
what is the SR made up of
longitudinal and terminal elements
where are the terminal cisternae of SR located
close to t-tubules
what are the terminal cisternae
where the SR meets the t tubules to form Ca2+ release site
why do atrial myocytes lack t tubules
the are not requires to produce as much force as ventricular myocytes
RyR2
ryanodine receptor 2, cardiac myocyte specific ryanodine receptor, cA2+ release channel
LTCC
L-type calcium channel, located in wall of t tubule
where do RyR2 and LTCC create a junction between and junction name
extraC and intraC calcium stores: Dyad junction
how does Dyad facilitate Ca2+ induced Ca2+ release
(cardiac excitation-contraction coupling)
packed full of channels to allow intra and extra coupling
what causes LTCCs to open
(cardiac excitation-contraction coupling)
AP travelling across surface membrane and depolarising t tubules
what causes RyR2s to open
(cardiac excitation-contraction coupling)
Ca2+ enters intracellular space between t tubules and SR through the LTCCs
what does the RyR2 channels opening cause
(cardiac excitation-contraction coupling)
Ca2+ flood out of SR to cytoplasm
what do spatio-temporal summation of Ca2+ sparks cause
(cardiac excitation-contraction coupling)
Ca2+ transient activating uniform and forceful contraction of the cell (individual calcium releases create a large coordinated calcium signal)
significance of the arrangement of RyR2 channels and what does this cause in the cardiac excitation-contraction coupling
causes a wave of Ca2+ release from SR which spreads along musculature
where are Ca2+ release sites located in the myocyte and why
z lines around myofibrils
means max diffusion distance to activate myofilaments in 500nm
allows synchronisation of contraction to be maintained
function of titin
associated with myosin
helps elasticity within I band
A band
thick filaments, mainly myosin
I band
thin filaments, mainly actin
tropomyosin
long protein associated with actin filament
lies in the groove made by two strands of actin filament
what are the three subunits of a troponin complex
Tn-C, cA2+
Tn-I, actin
Tn-T, tropomyosin
in the presence of Ca2+, what does the binding of Ca2+ to Tn-C cause
stronger binding of TnC to TnI
TnI can no longer bind to actin
cascade of binding changes
allows myosin to bind to actin
what happens when Ca2+ lowered again
Ca2+ ions dissociate from TnC
TnI will bind once again to actin and myosin binding site will be covered
three possible pathways of Ca2+ recycling
pumped back into SR
NA+-Ca2+ exchanger
sarcolemma Ca2+ ATPase
